Probing the origin of the iron Kα line around stellar and supermassive black holes using X-ray polarimetry

Asymmetric, broad iron lines are a common feature in the X-ray spectra of both X-ray binaries (XRBs) and type-1 Active Galactic Nuclei (AGN). It was suggested that the distortion of the Fe Kα emission results from Doppler and relativistic effects affecting the radiative transfer close to the strong gravitational well of the central compact object: a stellar mass black hole (BH) or neutron star (NS) in the case of XRBs, or a super massive black hole (SMBH) in the case of AGN. However, alternative approaches based on reprocessing and transmission of radiation through surrounding media also attempt to explain the line broadening. So far, spectroscopic and timing analyzes have not yet convinced the whole community to discriminate between the two scenarios. Here we study to which extent X-ray polarimetric measurements of black hole X-ray binaries (BHXRBs) and type-1 AGN could help to identify the possible origin of the line distortion. To do so, we report on recent simulations obtained for the two BH flavors and show that the proposed scenarios are found to behave differently in polarization degree and polarization angle. A relativistic origin for the distortion is found to be more probable in the context of BHXRBs, supporting the idea that the same mechanism should lead the way also for AGN. We show that the discriminating polarization signal could have been detectable by several X-ray polarimetry missions proposed in the past.     

Information on particle acceleration and transport derived from solar flare spectropolarimetry

The hydrogen Hα line has been found to be linearly polarized at some locations and times during a June 15th 2001 flare observed with THEMIS. This flare was accompanied by radio pulses and hard X-ray emission. Linear polarization is below the noise level in the flare kernels. However, it is present at the edges of these kernels, in the line center and near wings where the polarization degree exceeds 4%. The directions of polarization are not random but close within ±15° to the tangential and radial directions. This polarization can be due either to electron beams and their associated return currents or to electron and proton beams.     

Off-axis irradiation and the polarization of broad emission lines in active galactic nuclei

The stokes Monte Carlo radiative transfer code has been extended to model the velocity dependence of the polarization of emission lines. We use stokes to present improved modeling of the velocity-dependent polarization of broad emission lines in active galactic nuclei. We confirm that off-axis continuum emission can produce observed velocity dependencies of both the degree and position angle of polarization. The characteristic features are a dip in the percentage polarization and an S-shaped swing in the position angle of the polarization across the line profile. Some differences between our stokes results and previous modeling of polarization due to off-axis emission are noted. In particular we find that the presence of an offset between the maximum in line flux and the dip in the percentage of polarization or the central velocity of the swing in position angle does not necessarily imply that the scattering material is moving radially. Our model is an alternative scenario to the equatorial scattering disk described by Smith et al. (2005). We discuss strategies to discriminate between both interpretations and to constrain their relative contributions to the observed velocity-resolved line and polarization.     

Impact linear polarization observed in a UV chromospheric line during a solar flare

Linear polarization was observed in the S I 1437Å line in bright flaring points during the soft X-ray emission. The degree of polarization is about 25% and is detected at a signal to noise ratio of 2.9. The polarized electric vector is directed towards disk center to within 3°.This polarization could be due to collisional excitationm of S I by energetic electrons beamed in the vertical direction. We suggest that the heat flux in the region interconnecting the transition zone to the high chromosphere during the gradual phase of a flare could lead to an anisotropic excitation. Then the observed polarization would be due to vertical motions of the transition zone sweeping the preexisting chromosphere.     

太阳耀斑硬X射线高能时延和辐射展宽

本文从耀斑高能电子束流与太阳大气相互作用产生硬X射线辐射的基本事实出发,根据观测资料,提出了一个流量与能谱同步变化的注入源函数模型,研究太阳大气(靶物质)密度对耀斑硬X射线时间响应.理论计算与观测事实基本一致.主要计算结果如下:高能时延与辐射展宽是耀斑硬X射线轫致辐射时间特征的二种表现,硬X射线发射区的太阳大气密度越低,高能时延与辐射展宽效应越明显,二者之间存在显著的相关性.      

The STARK-B database as a resource for “STARK” widths and shifts data: State of advancement and program of development

“Stark” broadening theories and calculations have been extensively developed for about 50 years and can now be applied to many needs, especially for accurate spectroscopic diagnostics and modeling. This requires the knowledge of numerous collisional line profiles. Nowadays, the access to such data via an online database becomes essential. STARK-B is a collaborative project between the Astronomical Observatory of Belgrade and the Laboratoire d’Étude du Rayonnement et de la matière en Astrophysique (LERMA). It is a database of calculated widths and shifts of isolated lines of atoms and ions due to electron and ion collisions (impacts). It is devoted to modeling and spectroscopic diagnostics of stellar atmospheres and envelopes, laboratory plasmas, laser equipments and technological plasmas. Hence, the domain of temperatures and densities covered by the tables is wide and depends on the ionization degree of the considered ion. STARK-B has been fully opened since September 2008 and is in free access.     

Astrophysical motivation for X-ray polarimetry

In this paper I will review the motivation for measuring polarization in the X-ray band from astrophysical sources. Emission models designed to reproduce X-ray spectra can be tested using polarization, and polarization detected in other wavelength bands makes clear predictions as to the X-ray polarization. Polarization is a powerful tool to infer geometrical properties of sources which are too small to be spatially resolved. At the same time, there has been recent progress in instrumentation which is likely to allow searches for X-ray polarization at levels significantly below what was possible for early detectors. This paper will review the history of X-ray polarimetry, discuss some experimental techniques and the scientific problems which can be addressed by future experiments.     

Imaging polarimetry of Hα kernels of solar flares with a ferroelectric liquid crystal polarimeter

Impact polarization of the kernels of solar flares in the chromospheric lines is one of the important diagnostics of high-energy particles in solar flares. Even though so far the detection of polarization up to 10% have been reported by various authors, generally the polarization of the flare kernels is small. To detect the impact polarization, high-cadence imaging polarimetry with the precision of the order of 0.1% is required. The seeing-induced error is the greatest cause degrading the polarimetric precision, but it can be reduced by high-frequency polarization modulation. We developed a polarimeter with ferroelectric liquid crystals (FLCs) combining with a high-speed CCD camera, and the modulation frequency as high as 1 kHz realized the precision of the polarimetry in the Hα line of the order of 0.1%. Many flares have been observed with this polarimeter, and we found that just small flares sometimes show significant polarization. However, the majority of the flares do not show polarization signals larger than 0.1%. Our results suggest that there are some unknown parameters to produce the polarization of flare kernels.     

New model of hair cell bundle functioning in otoliths.

Transformation of the mechanical input in the chain: acceleration of otolithic membrane (OM)-displacement of the OM gel layer -deflection of hair cell bundle (HCB) -deformation of the system of tip-links- formation of temporal pattern of polarization was studied using simplified analytical models of these stages of conversion of mechanical stimulus into the HCB electrical response. The process of transformation of information in this chain was considered for two extreme cases of OM gel-HCB interaction: 1) the HCBs exactly follow the gel displacement; 2) stiff stereocilia and weak surrounding gel allow the relative motion of the bundle with regard to the gel. The analysis of a simplified model of cell polarization based on threshold triggering of the HCB tip-links allows to hypothesize that spatially nonhomogeneous HCB structure with a set of stereocilia of varying heights is designed to perceive spatially nonhomogeneous gel displacements caused by external acceleration. Thus, the HCB-OM gel interaction in the first case leads to formation of temporal pattern of depolarization that corresponds to the temporal pattern of gel displacement. In the second case the kinetics of depolarization reflects time dependence of gel displacement velocity.     

Energy and charge localization in irradiated DNA.

The relation between the site of energy deposition and the site of its biological action is an important question in radiobiology. Even at 77 degrees K, evidence is clear that these two sites must be separated since energy deposition is random but specific products are formed. Several processes that may contribute to this separation are: 1) hole migration and stabilization through deprotonation to give neutral oxidation product radicals; 2) electron trapping and transfer to form specific radical anions, possibly followed by protonation to give neutral reduction product radicals; and 3) recombination of spatially separated charges or radicals. These microscopic processes will be reviewed critically in an analysis using electron paramagnetic resonance spectroscopy (EPR) evidence for and against long-range transfer of energy and/or charge in frozen, hydrated DNA.     

利用偏振图像加权融合及CLAHE算法的水下成像方法

针对传统基于偏振差分原理的水下光学成像方法中目标退偏振特性差异引起的图像中局部反射光损失的问题,本文提出了基于偏振图像加权融合与限制对比度自适应直方图均衡（Contrast Limited Adaptive Histogram Equalization, CLAHE）算法的水下成像方法。一方面,将原始水下图像分解为偏振光强图像和非偏振光强图像,根据不同退偏振特性目标在两幅图像中的灰度值分布特点,设计相应的权重因子,对两幅图像进行加权融合。从而实现在压缩原始水下图像中散射光的同时,保留更多目标反射光,提升整体目标反射光在融合图像中所占的比例。另一方面,为了进一步提升融合图像的对比度,利用限制对比度自适应直方图均衡算法对融合图像进行处理。该算法能够在提升融合图像对比度的同时,有效避免图像噪声的放大。实验结果表明,相比于传统的偏振差分方法以及独立的直方图均衡化算法,本文提出的算法能够有效提升水下图像的清晰度和对比度。     

虚拟场景中半动态对象的层次运动模型

为了增强视觉沉浸感,虚拟场景中存在着大量的树木、火焰、烟尘等半动态对象.针对这类对象进行运动描述时计算开销大,严重影响仿真的实时性能的问题,提出一种层次运动模型LOM(Level of Motion).首先给出了半动态对象的定义;然后根据该类对象的特点提出了层次运动模型;最后以树木随风实时摆动行为的建模为实例,对该模型的有效性进行了验证.实验表明该模型的应用可以在保证虚拟场景视觉效果逼真的同时,使仿真获得较为理想的实时性能.      

Collisional excitation of vinylidene (H2CC)

Though H₂CO, H₂CS, H₂CCC, H₂CCCC, H₂CCO have been identified in cool interstellar molecular clouds, identification of H₂CC is still awaited. To analyze its spectrum, collisional rate coefficients are required. We have calculated collisional rate coefficients for rotational transitions between 23 levels of ortho and para H₂CC for kinetic temperatures 10, 20, 30, 40, and 50 K. The scattering problem is analyzed using the computer code MOLSCAT where the colliding partner is He atom. The interaction between H₂CC and He has been calculated with GAUSSIAN 2003. For the interaction potential obtained with GAUSSIAN 2003, MOLSCAT is used to derive the parameters q(L,M,M^′|E)$q(L\text{,}M\text{,}{M}^{\prime }|E)$ as a function of energy E   of the colliding partner. After averaging the parameters q(L,M,M^′|E)$q(L\text{,}M\text{,}{M}^{\prime }|E)$ over a Maxwellian distribution, the parameters Q(L,M,M^′|T)$Q(L\text{,}M\text{,}{M}^{\prime }|T)$ as a function of the kinetic temperature T in the cloud are obtained. Finally, the collisional rate coefficients have been calculated.     

PCB及元件的温度场有限元分析

首先简要介绍了一下热传输原理,而后应用有限元探索了双列直插式元件及印制电路板(PCB)的二维和三维稳态热传输,通过计算实例的温度场分布对两种方式作比较,并通过点测进行实验研究,计算与实验测量相吻合,给出结论, 有限元三维模拟比二维模拟更为复杂,但得到的信息更为详细.     

Shocks and instabilities in the partially ionised solar atmosphere

The low solar atmosphere is composed of mostly neutral particles, but the importance of the magnetic field for understanding observed dynamics means that interactions between charged and neutral particles play a very important role in controlling the macroscopic fluid motions. As the exchange of momentum between fluids, essential for the neutral fluid to effectively feel the Lorentz force, is through collisional interactions, the relative timescale of these interactions to the dynamic timescale determines whether a single-fluid model or, when the dynamic frequency is higher, the more detailed two-fluid model is the more appropriate. However, as many MHD phenomena fundamentally contain multi-time-scale processes, even large-scale, long-timescale motions can have an important physical contribution from two-fluid processes. In this review we will focus on two-fluid models, looking in detail at two areas where the multi-time-scale nature of the solar atmosphere means that two-fluid physics can easily develop: shock-waves and instabilities. We then connect these ideas to observations attempting to diagnose two-fluid behaviour in the solar atmosphere, suggesting some ways forward to bring observations and simulations closer together.     

GNSS geodetic techniques for time and frequency transfer applications

We performed an initial analysis of the pseudorange data of the GIOVE-B satellite, one of the two experimental Galileo satellites currently in operation, for time transfer.¹ For this specific aim, software was developed to process the GIOVE-B raw pseudoranges and broadcast navigation messages collected by the Galileo Experimental Sensor Stations (GESS) tracking network, yielding station clock phase errors with respect to the Experimental Galileo System Time (EGST). The software also allows processing the Global Positioning System (GPS) P1 and P2 pseudorange data with broadcast navigation message collected at the same stations to obtain the station clock phase errors with respect to the GPS system time (GPST). Differencing these solutions between stations provides two independent means of GNSS time transfer. We compared these time transfer results with Precise Point Positioning (PPP) method applied to GPS data in combined carrier-phase and pseudorange mode as well as in pseudorange-only mode to show their relative merits. The PPP solutions in combined carrier-phase and pseudorange mode showed the least instability of the methods tested herein at all scales, at few parts in 10¹⁵ at 1 day for the stations processed, following a tau^−½ interval dependency. Conversely, the PPP solutions in pseudorange-only mode are an order of magnitude worst (few parts in 10¹⁴ at 1 day for the stations processed) following a tau⁻¹ power-law, but slightly better than the single-satellite raw GPS time transfer solutions obtained using the developed software, since the PPP least-squares solution effectively averages the pseudorange noise. The pseudorange noise levels estimated from PPP pseudorange residuals and from clock solution comparisons are largely consistent, providing a validation of our software operation. The raw GIOVE-B time transfer, as implemented in this work, proves to be slightly better than single-satellite raw GPS satellite time transfer, at least in the medium term. However, one of the processed stations shows a combined GPS P1 and P2 pseudorange noise level at 2 m, a factor 2 worst than usually seen for geodetic receivers, so the GPS time transfer results may not be at their best for the cases processed. Over the short term, the GPS single-satellite time transfer instability outperforms the GIOVE-B by an order of magnitude at 1 s interval, which would be due to the different characteristics of the tracking loop filters for GPS P1 and P2 on one hand and the GIOVE-B signals on the other. Even at this preliminary stage and using an experimental satellite system, results show that the GIOVE-B (and hence Galileo) signals offer interesting perspectives for high precision time transfer between metrological laboratories.     

旋转光滑U形通道内流动和换热的数值模拟

数值模拟了旋转状态下涡轮叶片U形内冷通道湍流流场和温度场的分布,分析了流阻和换热的变化规律.结果表明,旋转状态下哥氏力、离心力和浮升力的共同作用使得流场发生了复杂的变化.旋转强化了换热,减小了流阻.但旋转使得换热在各个面换热能力分布不均,增加了温度梯度.      

Canadian landsat studies for monitoring hydrologic conditions and coastal environments: A summary

This report summarizes a major paper reviewing Canadian work using Landsat imagery for studying changes in lakes and in coastal environments. The nature of environmental change is discussed. For lakes and coastal environments, it is suggested that change is either seasonal, long term, short term or constant; examples of each are given. There is also an important distinction between natural and man-induced change. Outlined in the paper are studies of the filling of the LG2 Reservoir, water level and vegetation changes in the Peace-Athabasca Delta, possible vegetation changes due to the construction of Roberts Bank Port near Vancouver and measurement of surface suspended sediment concentration in the Bay of Fundy using chromaticity analysis.     

多传感器遥感图像数据融合研究

重点研究了卫星遥感图像融合技术.通过在Matlab平台上实现基于颜色空间变换和基于小波变换的图像融合算法,分析了颜色空间变换的融合特点,并结合高分辨率图像、多光谱图像以及SAR图像的融合结果对相关理论进行了验证;研究了基于小波变换的融合方法在不同分解和重构级数下所获得的融合图像的特征,比较了各级融合图像的特点和相互间的差别;通过对高分辨率图像和多光谱图像的融合实例,给出了达到融合目的所应进行的最低分解重构级数与两原始图像空间分辨率指标比值间的定量关系;分析了不同小波因子对融合结果的影响,并结合颜色空间变换方法的融合结果得出了最终结论.      

A comparison of quality factors and weighting factors for characterizing astronaut radiation exposures.

Radiation exposures are typically characterized by two quantities. The first is the absorbed dose, or the energy deposited per unit mass for specific types of radiation passing through specified materials. The same amount of energy deposited in material by two different types of radiation, however, can result in two different levels of risk. Because of this, for the purpose of radiation protection operations, absorbed dose is modified by a second factor intended to normalize the risk associated with a given exposure. We present here an inter-comparison of methods for this modification. First is the radiation quality factor (Q), as defined by ICRP publication 60. This quantity is related functionally to the unrestricted linear energy transfer (LET) of a given radiation, and is multiplied by the absorbed dose to derive the dose equivalent (H). The second method for modifying absorbed dose is the radiation weighting factor, also given in ICRP-60, or as modified in NCRP report 115. To implement the weighting factor, the absorbed dose resulting from incidence of a particular radiation is multiplied by a factor assigned to that type of radiation, giving the equivalent dose. We compare calculations done based on identical fields of radiation representative of that encountered by the MIR space station, applying each of these two methods.